US20120206733A1 - Method and system for the thickness data determination of ultrathin optical films in-situ - Google Patents

Method and system for the thickness data determination of ultrathin optical films in-situ Download PDF

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Publication number
US20120206733A1
US20120206733A1 US13/502,134 US201013502134A US2012206733A1 US 20120206733 A1 US20120206733 A1 US 20120206733A1 US 201013502134 A US201013502134 A US 201013502134A US 2012206733 A1 US2012206733 A1 US 2012206733A1
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Prior art keywords
film
thickness
radiation
interferometric structure
substrate
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US13/502,134
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English (en)
Inventor
Jarkko Antila
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Valtion Teknillinen Tutkimuskeskus
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Valtion Teknillinen Tutkimuskeskus
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Publication of US20120206733A1 publication Critical patent/US20120206733A1/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0625—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of absorption or reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0675—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating using interferometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0683—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating measurement during deposition or removal of the layer

Definitions

  • the invention relates to method and system for thin film thickness data determination, and, in particular, thickness data determination of ultrathin optical films such as of thickness changes in-situ.
  • a measurement method according to the present invention is characterized by features disclosed in the characterizing portion of the independent claim 1 describing the measurement method.
  • a system according to the present invention is characterized by features disclosed in the characterizing portion of the independent claim 8 describing the system.
  • a stability measurement, and optionally a calibration, method according to the present invention is characterized by features disclosed hi the characterizing portion of the corresponding independent claim.
  • a computer program product according to the present invention is characterized by features disclosed in the characterizing portion of the independent claim describing the computer program product.
  • thin film thickness related data e.g. thickness change
  • Said film is arranged, according to the invention, onto a substrate such that said film and a substrate in a whole form an interferometric structure.
  • the substrate is preferably such a base on the top of which said thin film is depositied by any deposition method known in the prior art.
  • optical radiation is emitted towards an interferometric structure, formed by a substrate and a film, and optically reflected from the said interferometric structure radiation is measured.
  • thickness related data for said film is then determined optically by means of the reflected radiation.
  • an interferometric structure formed by a film to be grown and a substrate is substantially an optical Fabry-Perot-interferometric structure.
  • film thickness related data is determined by means of said optically reflected radiation spectrum related information.
  • film thickness related data is determined optically, without a contact.
  • the spectrum is defined from said optically reflected radiation, to which said spectrum a theoretical spectrum is then correlated, said theoretical spectrum being calculated beforehand for at least one optical thickness value of an interferometric structure, in order to obtain e.g. an interferogram.
  • Thickness related data of a measured structure and then also of a deposited film is determined preferably by means of the interferogram's maximum point. Maximum point is preferably above a measurement cavity threshold value.
  • Thickness related data to be determined relates, in particular, to film thickness change for example when growing said film by some deposition method, such as e.g. Atomic Layer Deposition (ALD) or Chemical Vapor Deposition (CVD)-methods.
  • ALD Atomic Layer Deposition
  • CVD Chemical Vapor Deposition
  • the determination of thickness related data is accomplished by a correlation method.
  • a suitable correlation method of this kind is, for example, an Airy-function, but also other periodic functions, such as, e.g. cosine functions or box functions may be used.
  • the invention is not at all limited by correlation methods presented in here, but also other methods may be used.
  • the measurement noise may be significantly reduced, and a stable system in accordance with the invention may even reach a 10 pm optical path resolution.
  • Spectrum measurement itself can be performed, in accordance with the idea of the invention, also by means of prior art reflectometers, when a substrate film is used in combination with the correlation calculation.
  • the invention may be applied very broadly, for instance, for measuring the thickness of biofilms.
  • the invention may be applied very broadly, for instance, for measuring the thickness of biofilms.
  • the invention may be applied very broadly, for instance, for measuring the thickness of biofilms.
  • the invention may be applied very broadly, for instance, for measuring the thickness of biofilms.
  • an on-line spectrometer calibration for example of a Fabry-Perot-based spectrometer.
  • the invention offers significant advantages in comparison to solutions known from prior art.
  • An invention may be exploited, for example, in combination with ALD- and CVD-methods for thickness monitoring and—control in-situ.
  • the method further enables thickness measurement of films the thickness of which is below 1 nm, such as e.g. dielectric films, which is clearly below the level presented in the methods known from prior art.
  • the measurements, enabled by the invention provide a clear benefit e.g. for the developers of thin films processes as well as for thin film equipment controlling systems. Additionally, the hardware does not require particularly expensive components, so it is very cost effective and its measurement accuracy is excellent.
  • FIG. 1 illustrates an exemplary measurement arrangement according to an embodiment of the present invention
  • FIG. 2 illustrates two different cases of thin film formation around the original measurement cavity (cavity structure) by two different preparation methods
  • FIG. 3 illustrates an example of a simulated spectrum according to an embodiment of the present invention
  • FIG. 4 illustrates an exemplary correlation according to an embodiment of the present invention
  • FIG. 5 illustrates an exemplary simulated noise during cavity measurement according to an embodiment of the present invention
  • FIG. 6 illustrates an exemplary measurement cavity preparation according to some embodiment of the present invention
  • FIG. 7 illustrates an exemplary spectrometer, used in the measurement according to an embodiment of the present invention.
  • FIGS. 8 a - c illustrate an exemplary correlation method for thin film thickness data determination according to an embodiment of the present invention.
  • FIG. 1 illustrates an exemplary measurement arrangement 100 according to an embodiment of the present invention, wherein film 101 is deposited, for example, onto a selected substrate 102 .
  • an entity comprising a film and a substrate, forms an optical Fabry-Perot-interferometric structure.
  • This substrate and film combination is then measured optically without a contact, e.g. through window 103 , in which case it is not needed to supply the thin film device with extra equipment.
  • Thickness determination is accomplished by correlation method based on the spectral data, in which case an ⁇ ngström range resolution can be achieved. This enables measurement of e.g. one single-molecule layer formation in-situ.
  • an optical radiation of an exemplary system e.g. white light
  • an optical radiation source 104 is directed from an optical radiation source 104 via fiber 105 and via lens 106 to the measurement cavity located in chamber 107 , where light interferes and reflects back to the fiber.
  • Light further continues to spectrometer 108 , and data read therefrom is analyzed by correlation method, as, for example, by means of an Airy-function or other periodic function as cosine- and box functions.
  • Optical radiation source 104 may be a source generating e.g. white light or other continuous spectral radiation, like for example a halogen, or white LED, or other corresponding optical radiation source recognizable by those skilled in art.
  • a used optical fiber 105 may be, for example, an optical multimode fiber.
  • the film to be deposited is the same material as the measurement cavity. It should, however, be noted, that such an arrangement is by no means mandatory, but material combinations of another kind may be used.
  • the measurement cavity material may be e.g. one of the following: SiO 2 , Al 2 O 3 , Ta 2 O 5 , however, the invention is not limited only to these. Wherever reflection coefficients of a thin film and a measurement cavity do not differ greatly from each other, thus formed joint thickness may be easily calculated from the spectral data.
  • a method, in accordance with the invention is absolute, for instance, when the refractive indices of the material are known exactly, but, e.g. during ALD deposition formed molecular layers may be seen, according to the invention, directly on-line.
  • FIG. 2 illustrates two different cases of thin film formation around the original measurement cavity (cavity structure) 201 by two different preparation methods.
  • a film obtained from the CVD-instrument (for example, dielectric material) 101 a is formed on the other side of the test cavity, when again a thin film (for example, dielectric material) 101 b measured by ALD method (lower figure) covers the whole measurement cavity structure 201 .
  • FIG. 3 illustrates an example of a simulated spectrum 300 according to an embodiment of the present invention, when measurement cavity is (optically) 20 ⁇ m thick and also a 2 ⁇ m thick disturbance cavity is present, which can be caused by, for example, films formed on the window.
  • FIG. 4 illustrates exemplary correlation according to an embodiment of the present invention.
  • a theoretical spectrum calculated for at least one, but preferably several, cavity thickness values, is correlated to a measured spectrum, a depicted on FIG. 4 interferogram 401 is obtained.
  • An optical thickness of a measurement cavity with a thin film deposited is resolved by finding a pattern's maximum point above the known cavity threshold, for example, in case of FIG. 4 , by finding a maximum point only above a 5 ⁇ m threshold, in which case a maximum point is found at point 401 b, corresponding to about 20 ⁇ m thickness data.
  • a correlation may be implemented, in addition to the traditional Airy-function, also by the other periodic functions, like cosine- or box-functions.
  • FIG. 4 exemplary calculation method suits well only for above 5 ⁇ m optical thicknesses, however, the invention is not limited only to these.
  • FIG. 5 illustrates an exemplary simulated noise 500 during cavity measurement according to some embodiment of the present invention, when spectral signal to noise ratio is 1000. Measurement standard deviation is in this case below 0.1 nm.
  • FIG. 6 illustrates an exemplary method for a measurement cavity 600 preparation according to some embodiment of the present invention.
  • a support structure 601 from e.g. silicon may be used (upper figure), on the top of which again a film 601 b may be prepared by coating (middle figure).
  • a film may be e.g. an about 20 ⁇ m thick dielectric layer 601 b, which can be an aluminum oxide (Al 2 O 3 ), for example.
  • etching lower figure
  • a measurement cavity 600 may also lay directly on the silicon substrate.
  • FIG. 7 illustrates one of the exemplary spectrometers 700 , to be used in the measurement according to some embodiment of the present invention.
  • small grating spectrometers manufactured by Horiba may be exploited for the purposes in question.
  • Resolution of a spectrometer may be, for example, 5 nm, which is enough for a method in accordance with the present invention. It is, however, clear for those skilled in art, that also other spectrometers may be used to implement the invention's basic idea without changing it.
  • FIGS. 8 a - c illustrate an exemplary correlation method for thin film thickness data determination according to some embodiment of the present invention, wherein a small known spectrum 801 ( FIG. 8 a ) is applied to modulate a measurement spectrum 802 ( FIG. 8 b ). In this way even a small modulation may be calculated with correlation 803 ( FIG. 8 c ). From correlation depicted in FIG. 8 one can clearly observe that the cavity is about 33 ⁇ m.
  • a measurement spectrum may be, according to an example, processed by e.g. Blackman-Harris window function, in order to improve an interferogram 803 .
  • a Fabry-Perot based spectrometer's stability control and a thickness measurement are preferably combined; it is observed, that when e.g. a quite thick, low reflectivity film is set in front of the Fabry-Perot interferometer (to the optical path of the spectrometer), a hardly detectable (for example, FIG. 8 a ) cyclic variability is obtained to the spectrum.
  • a cavity value (value, indicative of an optical thickness of an interferometric structure and on the other hand also a film thickness indicative value) can be isolated once again by correlation calculation, and if the spectrometer arrangement is preferable and a cavity material is chosen properly, then this cavity value may be used in accordance with an embodiment of the invention for measuring a spectrometer's stability, optionally, for calibration.
  • So called modulation cavity may be, in its simplest, e.g. a single coating layer on the window of the chamber used.
  • the chamber used may be for example a metallic case or another chamber, where may be e.g. some gas atmosphere, such as, e.g. nitrogen atmosphere.
  • some gas atmosphere such as, e.g. nitrogen atmosphere.
  • a probable implementation scenario may be mentioned, wherein to the optical path an additional merely encapsulated or such substrate, the thickness of which is preferably less than of a measurement substrate, is arranged such that this reference thickness may be determined from an interferogram. Since this reference substrate remains unchanged, so all thickness variations from measured reference substrate are due to the spectrometer's “life” (thus describing also (non)stability), in which case with these data one can preferably compensate for the actual measurement. In practice this can be implemented also by an additional fiber branch and by a reference substrate reflection measurement.
  • a substrate is used, chosen to be sufficiently thick (e.g. 20 ⁇ m), so that, for example, a disturbing effect of a film accumulating on the chamber's window may be removed from the results.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)
US13/502,134 2009-10-15 2010-10-15 Method and system for the thickness data determination of ultrathin optical films in-situ Abandoned US20120206733A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI20096065 2009-10-15
FI20096065A FI20096065A0 (fi) 2009-10-15 2009-10-15 Menetelmä ja järjestelmä ultraohuiden optisten kalvojen paksuustietojen määrittämiseksi in-situ
PCT/FI2010/050806 WO2011045477A1 (en) 2009-10-15 2010-10-15 Method and system for the thickness data determination of ultrathin optical films in-situ

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EP (1) EP2488824A1 (ja)
JP (1) JP2013507635A (ja)
FI (1) FI20096065A0 (ja)
WO (1) WO2011045477A1 (ja)

Cited By (1)

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CN114449773A (zh) * 2022-02-11 2022-05-06 上海锦晟电子科技有限公司 一种dpc陶瓷基板测量方法、装置及设备和系统

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US7573582B2 (en) * 2003-09-05 2009-08-11 Kabushiki Kaisha Toshiba Method for monitoring film thickness, a system for monitoring film thickness, a method for manufacturing a semiconductor device, and a program product for controlling film thickness monitoring system

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JP2013507635A (ja) 2013-03-04
FI20096065A0 (fi) 2009-10-15
EP2488824A1 (en) 2012-08-22
WO2011045477A1 (en) 2011-04-21

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